1. Field of the Invention.
The present invention relates generally to surgical towels and drapes, and particularly to a towel or drape useful in avoiding loss of a patient's core body heat as a result of a prolonged operation.
2. Discussion of the Known Art.
Hypothermia, i.e., a drop in core body temperature below 36 .degree. C. (96.8 .degree. F.), has been known to occur in patients who have undergone extensive or prolonged surgery. Referred to as accidental, inadvertent, unintentional, intraoperative or perioperative hypothermia, the occurrence of this type of hypothermia is recognized in the medical field as a serious problem, giving rise to complications such as shivering, vasoconstriction and cardiovascular instability, particularly in older patients. For example, see M. D. Fallacaro, et al, Inadvertent Hypothermia, 44 ARON Journal (No. 1) at 54, et seq. (July 1986); and N. L. Burkle, Inadvertent Hypothermia, 10 Today's OR Nurse (No. 7) at 27, et seq. (July 1988).
There are several causes of unintentional hypothermia. Modern operating theatres are closely temperature controlled for the comfort of the surgeons and attendants. Typical operating room temperatures are maintained below 20 .degree. C. (68 .degree. F.), regardless of the number of hours extensive surgery may be carried out. The ambient temperature is therefore 16 degrees C. below the patient's core level. Because of this temperature imbalance, heat is lost from the patient's body by radiation through the open incision into the surrounding environs.
Further, the common practice of applying wet cotton towels on exposed organs and other areas of the surgical field, actually tends to promote body cooling by evaporation. That is, even moist heated towels will become cold by evaporative cooling.
Once unintentional hypothermia is diagnosed, it becomes very difficult to reverse the body cooling trend. Current methods of treating or preventing hypothermia have substantially failed to prevent further heat loss. Such methods include the following:
1. Raising the operating room temperature. PA1 2. Using portable radiant heating lamps. PA1 3. Use of warm blankets. PA1 4. Warming the patient mattress. PA1 5. Reflective blankets. PA1 6. Heated gases. PA1 7. Blood warmers. PA1 8. Fluid warmers. PA1 9. Irrigation with warm fluids.
In major abdominal surgical procedures, much serous viscera become exposed to the operating room environs and wetted cold towels. This condition is one in which evaporative heat loss becomes at least as great a factor that contributes to overall body heat loss, as does any radiative heat loss through the opened abdominal cavity. The various active patient warming techniques noted above therefore must overcome the combined radiative and evaporative heat losses if they are to avoid hypothermia resulting from protracted abdominal surgery.
A material sold under the name "Space Blanket" has been experimented with as a means of avoiding hypothermia in patients undergoing neurosurgery. See P. Radford, et al, Metallized Plastic Sheeting in the Prevention of Hypothermia During Neurosurgery, 51 Br. J. Anaesthesia 237 (1979); and J. Brunton, et al, Reduction of Heat Loss in Neurosurgical Patients Using Metallized Plastic Sheeting, 54 Br. J. Anaesthesia 1201 (1982).
Each "Space Blanket" consists of an artificial fibre layer with two outside layers of metallized plastics sheeting (m.p.s.). In the experiments, patients were wrapped with m.p.s. prior to surgery, but the immediate surgical field was left exposed. The reported results showed that as used, m.p.s. alone was not sufficient to maintain normal body temperature during surgery, and that active warming systems were needed to ensure normothermia.